1. Field of the Invention
The present invention relates to a sheet feeding mechanism for feeding a sheet-type recording medium, and a recording apparatus having the sheet feeding mechanism.
2. Description of the Related Art
In various types of recording apparatuses, as an example of structures of sheet feeding mechanisms for feeding a stacked sheet recording medium, a mechanism of an inclined surface separation system is known. In this system, the uppermost recording medium in horizontally stacked recording mediums in a sheet cassette is fed with a sheet feeding roller, and the uppermost recording medium is separated from the lower recording medium using an inclined surface provided at the downstream side of the conveyance direction to feed the mediums one by one.
In such a sheet feeding method, for example, a structure is discussed in Japanese Patent Application Laid-Open No. 2006-225151. This structure has been made by focusing attention on the point that recording mediums stacked at an upper part may slide out of a sheet cassette due to the force to attach the sheet cassette, in which the recording medium is stacked, to the recording apparatus. In this structure, a contact member for contacting the upper surface of the recording medium to prevent the movement of the recording medium is provided in a fixed manner on a sheet cassette attachment path at the recording apparatus side.
In another structure, a structure is discussed in Japanese Patent Application Laid-Open No. 2011-63369. Japanese Patent Application Laid-Open No. 2011-63369 discusses a structure for solving a problem that, in a sheet feeding operation with a sheet feeding roller, the feeding orientation of a recording medium to be fed from recording mediums stacked on a sheet feeding cassette is displaced, and the recording medium is fed in the skewed state. In this structure, a second roller is provided at the upstream side of the sheet feeding roller with respect to the sheet feeding direction to control the orientation of the recording medium, which is likely to be deformed, from above the recording medium to stabilize the orientation of the recording medium to be fed in the sheet cassette.
In Japanese Patent Application Laid-Open No. 2011-63369, with reference to FIG. 7 in the publication, a structure having a plurality of driven rollers provided to an arm including a feeding roller is also discussed. In this structure, the sheet feeding roller and the driven rollers contact the recording medium to press the recording medium to reduce a conveyance difference between the right and left sides in the width direction of the recording medium being fed by the sheet feeding roller at the downstream side in the sheet feeding direction. This structure prevents the recording medium fed from the sheet cassette from being inclined and fed (i.e., skewed).
Meanwhile, in the inclined surface separation system, for example, as illustrated in FIGS. 7 and 8, a recording medium 108 to be fed with a sheet feeding roller 110 contacts an inclined part 111 and the recording medium 108 is curved upward and conveyed. In such a state, in a portion 108m near the curving portion of the recording medium 108 and on the conveyance extended line of the sheet feeding roller 110, portions where the recording medium is bent may exist. In such a case, as indicated by the arrows, at portions 108s at the both ends of the recording medium 110 at the leading edge side in the conveyance direction, the recording medium 110 is deformed toward the center side of the recording medium.
In other words, when the sheet feeding roller 110 rotates while pressing a center portion 108C of the uppermost recording medium 108 stacked on a stacking portion 106, the uppermost recording medium 108 is conveyed in the conveyance direction. Then, the uppermost recording medium 108 is bent around the portion 108m of the recording medium 108 as the recording medium 108 advances upward along the inclined portion 111. In this state, depending on effects of the pressure of the sheet feeding roller 110, the bent posture (see the portion 108m in FIGS. 7 and 8) near the center portion of the recording medium 108 differs from the bent posture (see the portions 108s in FIGS. 7 and 8) at the both end portions of the recording medium 108. Specifically, the vicinity of the center portion of the recording medium 108 is bent at a position closer to the inclined portion 111 than the both end portions of the recording medium 108 is. Due to the differences in the bent postures in one recording medium 108, as illustrated in FIG. 8, distortion is generated at the leading edge portion of the recording medium 108.
Generally, the distortion disappears due to the stiffness of the recording medium as the sheet feeding proceeds and as an area (area of the recording medium contacting the inclined surface) of the recording medium having arrived at the inclined surface increases.
In the state the distortion exists, if the leading edge of the recording medium 108 is held in the nip formed by a rubber portion of a conveyance roller 112 and a pinch roller 113, wrinkles are formed in the recording medium 108.
Such a phenomenon is especially likely to occur in a recording medium having low stiffness such as thin paper.
To regulate such deformed conveyance of the recording medium, the structure discussed in FIG. 7 in Japanese Patent Application Laid-Open No. 2011-63369 may be employed. The structure is, however, directed to prevention of the recording medium from being fed in an inclined state, and the driven roller always contacts the recording medium with a regulating force (urging force) for regulating the recording medium from being inclined in the sheet feeding operation. As a result, a large load is applied to the driving force for sheet feeding. Further, while the structure is effective to reduce the skew, the strong pressure by the driven roller on the recording medium may cause occurrence of a bending portion like 108m illustrated in FIG. 8 also in the driven roller portion.
Further, the contact member discussed in Japanese Patent Application Laid-Open No. 2006-225151 is not configured to control distortion in a recording medium to be fed, and the contact member is fixed to the apparatus. As a result, depending on the number of stacked sheets of the recording medium, its functions are limited. Consequently, this structure is not effective to the problems to be solved in the present invention at all.